Generally, it is known that the addition of metal ion capturing agents, such as zeolites, to detergents reduces the effects of calcium ions and magnesium ions in tap water on surfactants, thereby removing dirt stains adhered to clothes, while the detergents inhibiting redeposition owing to freed dirt stains by making the washing liquid alkaline to increase dispersion of the dirt stains.
Therefore, in general, conventional detergent granules include alkalizing agents and metal ion capturing agents. The detergent granules are generally produced by the following method.
Specifically, a slurry comprising aqueous dispersion of surfactants, mainly comprising anionic surfactants and nonionic surfactant; alkalizing agents, such as sodium carbonate and sodium silicates; calcium ion capturing agents (metal ion capturing agents), such as zeolites and sodium tripolyphosphates; fillers, such as sodium sulfate; and other components (those which are stable against heat) is prepared. Thereafter, the resulting slurry is dried to be powdered. Subsequently, materials which are unstable against heat including perfumes, and in certain cases, bleaching agents and bleaching activators are post-blended, to give desired detergent granules.
Incidentally, phosphorus-based metal ion capturing agents typically exemplified by tripolyphosphates have been formulated in dry granules, the tripolyphosphates being generally employed as calcium ion capturing agents before the use of zeolites. This is due to the fact that the phosphorus-based metal ion capturing agents have a function of alkalizing agents besides the calcium ion capturing capacity and also have the most suitable properties for improvement in powder properties, such as flowability, of the dry granules.
In the detergent granules mentioned above, since the alkalizing agents, such as alkali metal carbonates and alkali metal silicates, also have the characteristics of improving flowability by mechanically strengthening the granules themselves, the alkalizing agents act to form into granules with surfactants having plasticity and zeolite fine particles, so that the alkalizing agents are generally included in the same granules as the surfactants and the zeolites.
As mentioned above, since the metal ion capturing agents and the alkalizing agents are formulated in the same granule in the conventional detergents, the dissolution of these components may simultaneously show alkalizing ability and metal ion capturing capacity in the washing liquid. In certain cases, the alkalizing ability is shown earlier than the metal ion capturing capacity because the rate of reaction of the metal ion capturing agents with calcium ions and magnesium ions in water is delayed more than the rate of reaction of an alkalizing agent and water. The same can be said for liquid detergents, and since the metal ion capturing agents and the alkalizing agents are mixed in the same liquid, the alkalizing ability and the metal ion capturing capacity may be simultaneously shown, or the alkalizing ability is shown earlier than the metal ion capturing capacity.
Aside from the above, most man-derived sebum dirt stains contain fatty acids. In the process of washing, calcium and magnesium together with fatty acids form a scum, thereby lowering solubility and inhibiting the dispersion of the dirt stains in water. In particular, the present inventors have found that the scum-formation rate becomes faster as the alkalization degree (pH) becomes higher, and that washing performance cannot be exhibited to its optimum in conventional washing methods.
On the other hand, besides ones mentioned above, several methods comprising dry-blending alkalizing agents as separate granules from detergent granules have been conventionally known.
For instance, (1) Japanese Examined Patent Publication No. 3-52798 discloses a method for producing detergent builders having a small bulk density comprising adding organic compounds, such as polyethylene glycols, to alkali metal carbonates and/or alkali metal sulfates; and granulating the resulting mixture. In this publication, however, the purpose is to improve the granular strength and the solubility, not to increase the detergency effects by making the dissolution of the alkalizing agents delayed more than that of the metal ion capturing agents. Therefore, the alkalizing agent particles shown in Examples contain a small amount of a binder, and the polyethylene glycol has a low molecular weight, never teaching a delayed exertion of the alkalizing ability.
(2) Japanese Patent Laid-Open No. 55-52396 discloses a method of dry-blending particular alkali metal silicate granules to detergent granules containing surfactants and chelating agents, such as zeolites. In this publication, however, the purpose is to prevent the formation of water-insoluble materials owing to mutual interactions between silicates and zeolites and to maintain anti-corrosive effects on the washing machines, but not to increase the detergency effects by making the dissolution of the alkalizing agents delay more than that of the chelating agents. Therefore, the silicate granules shown in Examples have a large particle size, but they are not intended to delay the alkalizing ability by changing the particle sizes.
(3) Japanese Patent Laid-Open No. 62-167399 discloses a method for producing detergent granules having a high bulk density by limiting the amount of water-soluble, crystalline inorganic salts in the detergent base materials and dry-blending alkalizing agents with detergent granules in order to prevent the decrease in solubility of the detergent granules by increasing bulk densities thereof. However, for the same reasons set forth in (2) above, this publication does not suggest the increase in the detergency effects by making the dissolution of the alkalizing agents delay more than that of the metal ion capturing agent.
(4) Japanese Patent Laid-Open No. 58-213099 discloses a method for producing clothes detergents comprising dry-blending sodium carbonate with spray-dried powdery detergent base materials, the sodium carbonate having a particular density, particle size, and particle size distribution. The purposes of this publication, however, are to improve caking resistance and to prevent classification of sodium carbonate, and not to increase the detergency effects by making the dissolution of the alkalizing agents delay more than that of the metal ion capturing agents. Therefore, even in Examples, sodium silicate is included in the detergent base materials in relatively large amounts, the sodium silicates being incorporated in the same granules as zeolites, which are metal ion capturing agents.
Accordingly, there are no prior art references having the purpose of exhibiting an alkalizing ability to be delayed more than that of the metal ion capturing capacity. In the methods of post-blending alkalizing agents as described above, the alkalizing agents are blended simply for the following purposes: Since the zeolites are water-insoluble, the alkalizing agents are added for preventing the zeolites to remain on fibers caused by the action of the silicates to suppress the dispersion of the zeolite in cases where the zeolites are blended with silicates in the form of fine particles. Also, the alkalizing agents are added to improve caking resistance and solubility of the detergents. Moreover, in the conventional detergents mentioned above, since the alkalizing agents directly contact the washing liquid, the initiation of the alkalizing effect is faster than the case where the metal ion capturing agent and the surfactants are formulated in the same granules.